In an information recording medium, such as a CD (Compact Disc) and a DVD, a content protection function is incorporated. For example, a DVD format is constructed such that record contents can be reproduced only by a reproducing apparatus capable of performing decryption, by writing information about an encryption key in a lead-in area. Namely, it is designed such that each of a DVD video and DVD reproduction equipment has a “key” for performing the decryption, and only if the keys match, descrambling is performed, and video images can be normally reproduced.
However, lately, not only such a read-only DVD for recording contents (e.g. a DVD-Video), but also a DVD-R (Recordable) capable of writing only once, or a DVD-RW (Rewritable) capable of writing repeatedly are commercially available. Thus, if general disc data, including the encryption key information, is read from the DVD-Video or the like, as a RF signal, and it is hard-copied onto another recording medium, such as the DVD-R and the DVD-RW, the contents are illegally copied from the original DVD.
As a countermeasure against the illegal copying, a patent document 1 discloses a technology of forming embosses in an area out of the writable DVD where the encryption key information is recorded, in copying a DVD-Video or the like, such as the DVD-RW, to thereby make the area non-overwritable in advance. According to this method, the information is copied with the encryption key information lacked, so that it is extremely difficult to decrypt and normally reproduce the copied information.    Patent document 1: Japanese Patent Application Laid Open NO. 2000-331412